It is conventional practice to route the exhaust gases from the exhaust manifold of an internal combustion engine through a catalytic converter, then through a muffler and finally to the tail pipe and to atmosphere. Of course, the purpose of routing the exhaust gases through a muffler is to reduce engine noise. While this is desirable and even necessary for conventional use, that is street use, the back pressure caused by the exhaust gases passing through a muffler results in a loss of efficiency which can adversely affect engine performance. Many high performance engines operate most efficiently when the muffler is removed or bypassed. While this improves engine performance, the result in noise from the engine will likely prohibit use of the vehicle where unrestricted engine noise is not desirable or even prohibited. Therefore it would be very desirable to have a muffler which is operable in both a muffled or unmuffled mode. That is, in a muffled mode the muffler would utilize the silencing means in the muffler which would limit the sound level of exhaust gas noises to a legally permissible level. In the unmuffled mode, the silencing means would be bypassed so that the exhaust gases can be conducted to the atmosphere without any significant resistance from the muffler.
U.S. Pat. No. 1,766,973 (Beck) discloses a two part muffler. A so called "container" is connected to the outer end of an exhaust pipe. This container is basically a straight-through pipe which has a butterfly valve positioned at one end. Opening the butterfly valve permits the exhaust gases to escape directly to the atmosphere without muffling. The system also includes a diagonal pipe which is connected to the central portion of the container and extends for a distance from the body of the container. This pipe contains a number of baffle plates which are designed to muffle the gases that escape from the container through the pipe. Thus, if the driver wants to get the effect of a straight through pipe, the butterfly valve is opened which allows most of the exhaust gas from the engine to pass directly to atmosphere in an unmuffled state. If muffling of the sound is desired, then the butterfly valve is closed, and the gas passes through the pipe which contains baffle plates.
U.S. Pat. No. 1,840,082 (Breer) discloses a muffler in which the exhaust gas may pass directly through the muffler or maybe diverted through chambers in the muffler which deaden the noise of the exhaust gases. The muffler assembly uses a butterfly valve to allow exhaust gases to pass through a muffler in what is basically an unmuffled situation. If the butterfly is closed, some of the exhaust gases then pass through expansion chambers in the muffler and are thereby muffled.
U.S. Pat. No. 3,749,199 (Weber) discloses an exhaust gas muffler which is constructed such that the exhaust gas can be passed through the muffler for silencing or it can bypass the silencing means in the muffler and be exhausted directly to atmosphere with little or no resistance. The muffler system utilizes covers to close off portions of the exhaust system and exhaust gases are then passed through portions of the muffler for silencing. If the vehicle is to be utilized in a race, for example, then the covers are removed from certain of the exhaust pipes and the exhaust gases are conducted directly from the engine to atmosphere.